1. Technical Field
This invention relates to the field of electric utility power conditioning, and more particularly to power conditioners which involves a) maintaining voltage amplitude on the output to the load constant while an input utility voltage amplitude varies, and b) attenuating any distortions present in the input utility voltage waveform to the output.
The universality of the power conditioner of the present invention is in its ability to condition electric power delivered by different electrical services like 208/120 V dual phase service with two phases having phase shifts of 120 or 240 degrees; 240/120 V split phase service with two phases having phase shifts of 180 degrees; or single phase service with any voltage like 200 V, 208 V, 220 V, and 240 V. The frequency of any service can be any frequency used in the world, namely 50 or 60 Hz nominally, but generally in the range of 45 to 66 Hz.
2. Related References
Related references in the present invention's field include power supplies, power conditioners, and uninterruptible power supplies (UPS). Three patents have been found which are closely related to this subject.
U.S. Pat. No. 5,017,800 to Divan describes an electronic circuit which acts as a single phase power conditioner or UPS for only one type of electrical service - single phase with one grounded conductor (neutral). The main disadvantage of using this circuit is that output voltage shall be always smaller than the input voltage. This is a significant problem because the majority of power related problems are undervoltages and sags. Because the purpose of the power conditioner is to regulate the output at nominal nominal service value, like 120 V or 208 V, the conditioner will not be able to do it alone when input voltage is below nominal, undervoltage. Divan suggests using a transformer to amend this problem, see FIG. 4, but this greatly diminishes the value of the invention because the transformer's weight and size far exceed the weight and size of the electronic portion of the device. The use of the transformer also increases cost to such an extent that the smaller number of power semiconductor switches claimed in this invention versus similar purpose instruments does not provide for a total cost advantage. Regardless of these disadvantages, Divan can not be used for dual phase and other services, and therefore can not be a universal service conditioner/UPS.
U.S. Pat. No. 4,935,861 to Johnson et al. describes an invention almost identical to Divan's with capacitors C1 and C2 used instead of the active switches S1 and S3 used in Divan's invention. This invention has all the same disadvantages as Divan's plus one more. In Divan's invention, the waveform of the input current has limited control by switches S1 and S2 in such a way that the current can be sinusoidal in waveform and therefore input power factor values close to unity can be realized. Conversely, in Johnson's invention, the input circuit acts as a regular rectifier with capacitive filter, C1 and C2. It is well known that the input power factor of such a circuit is low, generally in the range of 0.4 -0.6. The current waveform is very distorted from sinusoidal and therefore there are large current harmonics which cause significant overheating of neutral conductors in the building wiring. This is one of the most frequent causes of building fires.
U.S. Pat. No. 4,934,822 to Higaki describes an AC-AC power supply acting as a power conditioner. This invention is an improvement over U.S. Pat. No. 4,827,151 to Okado. Okado's problem was that high frequency switching noise was generated on both output power conductors, compared to the grounded input conductor of Higaki's FIG. 2. Higaki's invention eliminated this high switching frequency component but left other signals on both output power conductors shown in FIGS. 4C and 4D. Those signals have sharp edges which contain high frequency harmonics that cause different problems in connected loads, like computer malfunction, magnetic component overheating, etc. All loads are designed to operate from sine waveform voltages on any power carrying conductors. Therefore this invention can hardly be used alone as a power conditioner, but only in conjunction with an isolation transformer which can eliminate this problem called "common mode voltage" Because of this disadvantage, Higaki can not be applied for universal service applications.